1. Field of the Disclosure
The technology of the disclosure relates to out-of-substrate package structures having electrical devices along with assemblies, wherein the out-of-substrate package structures may be mounted on electrical substrates and are advantageous for high-speed applications.
2. Technical Background
Benefits of communications networks having optical fibers supported by electrical components include extremely wide bandwidth and low noise operation for the optical signals transmitted on the optical fibers. However, these hybrid applications typically require converting the optical signal to an electrical signal and vice-versa. The electrical assemblies and devices used for converting signals between the optical and electrical domains and may be mounted upon an electrical substrate such as a printed circuit board or the like. The ability to convert data faster from optical signals to electrical signals and back again is needed as the demand increases for network speed, but as conversion speed increases obtaining a suitable signal becomes challenging. Consequently, current electrical devices electrically coupled on conventional out-of-substrate package structures mounted on electrical substrates are limited as to the speeds by which they can operate and still meet the desired specifications. As many of the applications of those conventional out-of-substrate package structures require large quantities of the out-of-substrate packages, improvements in the speed of transforming optical signals to electrical signals need to be cost effective while still meeting the desired performance. An example of one of the electrical devices may be, for example, an electro-optic device such as VCSELs or photodiodes on the out-of-substrate package that communicate with an optical fiber or the like.
FIG. 1 depicts a conventional technique to connect an electrical device 16 to a printed circuit board (PCB) 10 and into a position that is L1 above the PCB 10. In this technique, a conventional lead frame comprising the ground lead 12 and the signal lead 14 may be created. The ground lead 12 and the signal lead 14 may be bent, then directly soldered to the PCB 10. The ground lead 12 may be connected to ground connection 18 of the PCB 10 and the signal lead 14 may be connected to a signal connection 20 of the PCB 10.
As depicted in FIG. 1, electric lines e1 extending from the signal lead 14 terminate predictably on the ground lead 12 as shown by relatively linear electric line trajectories. In contrast, electric lines e2 created on the signal lead 14 tend not to terminate on the ground lead 12, resulting in large deviations in impedance away from standard impedances, for example fifty (50) ohms. The termination of the e2 lines is more difficult to control as electrical frequencies increase. In other words, a low-frequency electrical device is not as sensitive as a device operating at a frequency of five gigahertz (5 GHz) or more. When the impedance of the lead frame, including the electrical device 16, is not matched to the energy source then there is inefficient energy transfer between the electrical substrate, and the inefficiency of energy transfer is commensurate on the mismatch amount. The inefficient energy transfer manifests itself in signal reflections which may compromise signal integrity. Impedance matching between the PCB 10 and the electrical substrate becomes more important at higher signal speeds when impedance mismatches result in higher rates of signal reflections which degrades signal integrity below specifications.
In this regard, there is an unresolved need for improved approaches for assemblies and methods to electrically couple a high-speed electrical device to an electrical substrate, such as the PCB, in a cost effective manner.